1. Field of the Invention
The present invention relates to cure accelerators suitable for use in accelerating the cure of epoxy resins, in particular, to the acceleration of the imidazole cure of epoxy resins.
2. Description of Related Art
Epoxy resins are widely used as matrices for fiber-reinforced composite materials. These assemblies are widely used as structural components, in industrial and leisure applications, in aerospace and for transportation applications. Epoxy resins are also used in encapsulation formulations for the isolation and immobilization of electronic components as well as in structural adhesives.
There are a number of well-known reaction mechanisms which can be used to cure epoxy resins. One such mechanism involves the use of an agent which behaves as an initiator for the ring opening polymerization of the epoxy ring. Ring opening polymerization can be initiated by a number of compounds, common examples of which include tertiary amines and imidazoles.
Imidazoles offer significant benefits when used as epoxy resin curatives. The correct choice of imidazole enables the cure conditions to be manipulated, which can give benefits in outlife, reaction enthalpy, reaction rate, cure temperature, cost, mechanical performance and formulation viscosity etc.
For some applications it is important to have an epoxy resin system which cures rapidly at relatively low temperatures, for example 60-80° C., but that will maintain the properties referred to above. The majority of currently available imidazole-cured epoxy resin formulations fail to cure within practically useful timescales at low temperatures. Where it is possible to meet the required cure times using existing imidazole/epoxy chemistry, there are often times where a more rapid initiation of the cure reaction is of benefit. Preferably, this will be manifested as a faster gel time resulting in quicker structural immobilisation of the resin or assembly.
For some applications it is important to have an epoxy resin system which cures rapidly at relatively low temperatures, for example 60-80° C., but that will maintain the properties referred to above. The majority of currently available imidazole-cured epoxy resin formulations fail to cure within practically useful timescales at low temperatures. Where it is possible to meet the required cure times using existing imidazole/epoxy chemistry, there are often times where a more rapid initiation of the cure reaction is of benefit. Preferably, this will be manifested as a faster gel time resulting in quicker structural immobilisation of the resin or assembly.
Until recently, there have been no compounds available that can act as accelerators for the imidazole-epoxy reaction.
WO 02/081540 discloses the use of alcohols as imidazole cure accelerators in Resin Transfer Moulding (RTM) systems. However, alcohols are volatile and so their use as accelerators is unsuitable for many applications, particularly those applications where the alcohol has the opportunity to evaporate prior to or during cure.
Therefore, it is an object of the present invention to provide imidazole cure accelerators for epoxy resins which facilitate rapid low temperature cure of the resin.